In the development of new photographic or other coated products, many coating events must be run in order to determine the optimum coating formulation. Each coating event or run can be thought of as a "widget of knowledge" about an experimental photographic or other coating system. To achieve accelerated research and development, more knowledge must be acquired in less time. The present invention achieves this accelerated research and development knowledge in a novel manner.
In addition, two other factors impact research and development productivity, precision and experimental design. Greater precision allows the researcher to make valid decisions with fewer replicates. Good experimental design maximizes the informational value of each variation. The present invention also allows greater precision and improved experimental design.
The typical mode of operation for a photographic research and development person is to have one coating "slot" per week on a particular coating machine. During this coating period, 25 to 35 coatings can be made. Each of these coatings yields a "widget of knowledge". If the individual researcher could make more coatings with greater precision, his or her productivity would be increased.
However, certain constraints must be met in order to ensure a series of coating experiments is successful. The first is that a constant volumetric flowrate of fluid must be delivered to the web or support at all times. This includes both during the good coating interval as well as the transition interval while switching from one coating composition to the next. By delivering a constant volumetric flow to the web, dryer equilibrium is maintained. This translates to a constant drying profile for the web. A constant drying profile is desirable because the researcher wishes to maximize his ability to detect photographic differences caused by the composition changes in the coating, not from the drying profile induced differences. The drying profile is typically assumed to be constant.
Another constraint that faces the researcher trying to run a number of coating compositions is that the coating composition must continuously be applied to the web. If the operator lifts the hopper off of the web, not only is the dryer equilibrium disturbed, time is required to reestablish the coating bead when the hopper is put back in communication with the web. This applies to both a bead coating and curtain coating operation. If the operator leaves the hopper in communication with the web and pumps at purge rates, i.e. high flow rates, the coating machine dryer will become fouled. The coating composition would run off the edge of the web and the web would not be dried during windup. If the hopper was purged with water, the water would also run off the edge of the web. If the total flow during purges were redirected to waste, the coating bead or curtain would be broken requiring restart time. Air would inevitably get into the hopper making restart even more difficult. All the alternative hopper-in methods of composition changeover destroy dryer equilibrium. The present invention presents a method which meets the above constraints and allows the researcher to maximize the number of coating compositions coated onto a web in a minimum amount of time.